I used to dabble a bit with painting, even to the point of using an airbrush. The last serious thing I painted was a huge canvas with my then five year old daughter, Kelsey, and Mickey Mouse. Kelsey is now 22, so that tells you how long it's been. Yes, I'm very rusty now.
I still have several brushes, inclusing a Paasche VL5, a Turbo, and a couple of cheaper "t-shirt" brushes. In my opinion, the best paint for t-shirt was, and still is, Deka PermAir.
Deka has a wide colour range, and it is easy to work with. It cleans up quickly between colors, and mixes and thins well. One of the things I particularly liked was the colors were consistent, so if you ran out of orange, the next jar would not look like a different tint. I also thought it layered well, a must when doing detailed or complex work.
Thanks to the bad economy, Deka ended up folding their PermAir line. The closest I could come to Deka's quality was Wicked or 1-Shot. I still have a couple of jars left, should I ever want to goof around with airbrushing shirts again.